EP0702817B1 - Vorrichtung zur verbesserung der schärfentiefe eines strichmarkierungslesers - Google Patents

Vorrichtung zur verbesserung der schärfentiefe eines strichmarkierungslesers Download PDF

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Publication number
EP0702817B1
EP0702817B1 EP94921931A EP94921931A EP0702817B1 EP 0702817 B1 EP0702817 B1 EP 0702817B1 EP 94921931 A EP94921931 A EP 94921931A EP 94921931 A EP94921931 A EP 94921931A EP 0702817 B1 EP0702817 B1 EP 0702817B1
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EP
European Patent Office
Prior art keywords
segments
light
mask
along
dimension
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EP94921931A
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English (en)
French (fr)
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EP0702817A4 (de
EP0702817A1 (de
Inventor
Anna M. Quinn
Jay M. Eastman
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PSC Inc USA
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PSC Inc USA
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
    • G06K7/10544—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation by scanning of the records by radiation in the optical part of the electromagnetic spectrum
    • G06K7/10792—Special measures in relation to the object to be scanned
    • G06K7/10801—Multidistance reading
    • G06K7/10811—Focalisation
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K2207/00—Other aspects
    • G06K2207/1013—Multi-focal

Definitions

  • the present invention relates to a system for shaping a laser beam within a bar code scanner, so as to enhance the working range over which the bars of a bar code can be resolved thereby including reading of both close in and far out bar codes, and particularly to a system / method for controlling optical beam propagation, depth of focus and beam cross-section in a manner which is adapted to increase the resolving power of a bar code scanner, that is to minimize the beam size in the scanning direction (across the width of the bars of the code) from which the symbol represented by the code can be recognized in response to light returned to the scanner from the code.
  • the invention is especially suitable for use in bar code scanners which read code made up of bars which are generally rectangular with laser beams; however the optical beam shaping and amplitude control techniques and apparatus (diffractive optics) provided by the invention may be found generally useful wherever it is necessary or desirable to control the propagation of an optical beam and the shape thereof.
  • the present invention is an improvement over the methods and apparatus of optical beam shaping by diffractive effects as described in US Patent No. 5,200,597 issued April 6, 1993 to Eastman et al.
  • the methods and apparatus described in the patent are also generally discussed in an article by Eastman et al. which appeared in Optics and Photonics News, volume 3, No. 9 pages 25-31 on September 1992.
  • the patent describes optics employing far field diffraction to shape a laser beam from a laser diode and maintain its aspect (length to width) ratio constant over a distance in front of the scanner.
  • the '597 patent discloses how the size of an aperture which diffracts the beam may be selected to locate regions of near field and far field diffraction due to the aperture.
  • the '597 patent defines the Fresnel distance.
  • the Fresnel distance may be thought of as the distance along the optical axis from the aperture to the point at which the first Fresnel zone is equal in size to the aperture size, and is given by the square of the aperture radius divided by the wavelength of the light.
  • the '597 patent also points out that the Fresnel distance increases with aperture size.
  • a plot is also provided which relates the size of the beam to the size of the aperture and shows that , the beam size decreases in the near field region due to near field or Fresnel diffraction and increases linearly in the far field due to Fraunhoffer diffraction.
  • the Eastman et al. patent represents an advance in the art of beam shaping and control especially for bar code scanners over prior devices which use physical apertures to shape a beam by cropping. See Eastman et al. Patent 4,603,262 issued July 29, 1986 and US Patent 4,816,660 issued March 28, 1989.
  • US 4,808,804 discloses bar code symbol readers with variable spot size and/or working distance.
  • the apparatus includes a bar code scanner with an adjustable focal distance.
  • the scanner comprises a laser and an optical element which has an opaque zone and two slits.
  • the optical element is rotated in front of the laser such that the beam passes through one of the slits.
  • a smooth or a defined e.g. symmetric or sinc (sin x/x form)
  • a system for shaping a laser beam within a bar code scanner as defined by claim 16.
  • a system / method for control of beam propagation and shape which is especially adapted for use in a bar code scanning device, is operative to shape a laser beam which scans the bars of the code to a cross-section with a resolving dimension in the scanning direction across the bars of the code which is sufficiently small to read the code over a certain working range relative to a window of the scanner from which the beam projects.
  • a mask is used in the path of the beam, preferably in the vicinity of a lens which converges the beam to a geometric focus at a distance at least equal to the Fresnel distance of the element which is the beginning of the far field diffraction region prescribed by the element when illuminated by collimated light (A 2 /4 ⁇ , where A is the aperture diameter and ⁇ is the wavelength of the light).
  • the mask has at least two segments of different transmissivity through which the beam passes.
  • the segments are preferably provided by a plurality of concentric or symmetrically arranged segments, the symmetry being with respect to the axis of the beam propagating through the mask.
  • the segments are sized in a direction along the resolving dimension to be in predetermined relationship to each other.
  • the relationship is defined by the regions of near and far field diffraction, which due to one segment being of smaller size, overlaps the near field region of diffraction of the segment of larger size. It is believed that the transmissivity as well as the size combines so as to smooth the profile of the cross-section of the beam over the working range.
  • the smaller and larger segment sizes are selected so that their near and far field diffraction regions overlap at a point defined by a beam size which remains generally less than or equal to a desired size over a significant working range (an effective depth of focus).
  • FIG. 1 there is shown a laser diode 10 of the type which produces a beam which diverges mores rapidly (at a greater angle) with respect to a horizontal line perpendicular to the optical axis 12 and indicated at 14 in FIG. 1 than a vertical line (perpendicular to that horizontal line).
  • the system of the invention may utilize a beam having a circular cross-section rather than an elliptical cross-section as shown, but can work with elliptical beams which have their resolving axes coincident with the minor axis of the ellipse (the dimension w) as shown in FIG. 4.
  • the beam projects through a lens 20 (an "optical element") which may be a gradient index (grin) lens as described in the above-reference patent 5,200,597.
  • This lens is preferably used to provide a slightly converging beam.
  • the lens 20 and a mask 22 provide optic means for controlling the propagation and shaping the beam in accordance with the invention.
  • the mask 22 is in the vicinity of the lens. It is also spaced from the principal plane of the lens where it starts to converge the beam. This principal plane is indicated at 16 in FIG. 1. It has been found to be desirable to use a focused beam with a geometric image distance at a point equal to or farther than the Fresnel distance.
  • the mask 22 may be placed in abutment with the end, or deposited on the surface, of the lens 12 as shown in FIG. 2.
  • the mask may also be formed by varying the transmissivity of the lens material across the physical aperture of the lens, e.g., by diffusion of optically absorbing ions, or diffusion of dye into a plastic optical element. In any of these cases, it operates to present a plurality of apertures across the beam.
  • These apertures are preferably segments of a transmission mask of different transmissivity.
  • Bi-segmented transmission masks are shown in FIGS. 4, 5 and 6 and a tri-segmented mask is shown in FIG. 7.
  • the segments are radially symmetric with respect to the optical axis 14 and have inside segments 25, 27, 29 and 31 and outside segments 24, 26, 28, 30 and 32, 34 the inside and outside segments are of different transmissivity.
  • the mask through the varying transmissivities of the segments, apodizes the beam 18 and thereby enhances the resolving power of the beam 18.
  • apodization see Eugene Hecht & Alfred Zajac, OPTICS 413 (1979).
  • the inside segments may be clear (100% transmission) while the outside segments may be partially opaque, for example 50% transmissivity. Conversely, the outside segments may be of higher transmissivity than the inner segments.
  • the segments are stripes in the case of FIG. 4 with end regions 36 and 38 which are near the ends of the major axis of the beam 18. These end regions 36 and 38 are completely opaque (OP).
  • the mask of FIG. 5, with a circular inside area may have opaque ends 40 and 42.
  • the circularly symmetric mask of FIG. 6 may have a circular outside opaque area 44.
  • the mask of FIG. 7 has segments which are generally rectilinear in cross-section with opaque ends 48 and 50. These outer most boundaries of the mask may be formed by the physical aperture of the lens or its mount, rather than by the mask itself.
  • the horizontal axis of the masks coincides with the major axis of the beam when the masks are properly aligned with the beam.
  • the invention enables the resolving power to be maintained by using mask aperture segments of different effective size.
  • the mask aperture segments on the inside have an effective size (a) while the segments provided by the outside apertures have an effective size (A).
  • the inside aperture size for the mask of FIG. 5 is the diameter of the inside circular clear area 27.
  • the outside segment 28, as measured between the opaque areas 40 and 42 is of the dimension (A).
  • the mask of FIG. 6 has an effective segment diameter (a) for the inside circular area 29 and an effective segment diameter (A) for the diameter of the outside segment 30.
  • the mask of FIG. 7 has three successively larger areas.
  • the central area 31 being of size (a), the segments 32 and 34 increasing the size to (A) and the third segment 35 providing a segment area (B).
  • the beam width determining dimensions or sizes are along the major axis of the elliptical beam 18. Since the beam flips 90° in the far field diffraction region, as shown and explained in the Eastman et al. Patent 5,200,597, the beam size determining dimensions of the mask are along the major axis of the beam 18. The masks which are not circularly symmetric must be oriented with respect to the axes of the beam.
  • FIG. 3A shows an optical assembly including the optic means which provide beam propagation, control and shaping which is similar to the assembly illustrated in the Eastman et al. Patent (FIG. 8). It includes an outer barrel 60 which captures the laser diode 10 and an inner barrel 62 which is screwed or otherwise fit into the outer barrel with the mask 22 properly aligned with respect to the beam 18 as shown in FIGS. 4-7.
  • the mask 22 is in abutting relationship with an end of the lens 20.
  • the transmission mask may also be deposited onto the end of the lens or incorporated in the material of the lens, as described above.
  • the laser diode 10 is also captured in an outer barrel 64. It is biased against a lip 66 of the outer barrel by a spring 68 captured in a cylindrical slot in an inner barrel 70.
  • the mask is spaced along the optical axis from the end of the lens 20. While the lenses 20 in FIGS. 3A and 3B are shown as GRIN lenses, they may be conventional, spherical or aspheric lenses.
  • FIG. 3C shows a hand held scanner in schematic form where the optic means and laser diode assembly of FIGS. 3A or 3B are shown at 72 on a printed circuit board 74.
  • the beam from the assembly 72 is incident on a mirror 76 and reflected to a scanning, oscillating mirror 78, oscillated by a motor 80.
  • the scanning assembly is contained within a housing 82 having a window 84 through which the beam projects to the code.
  • the light returned from the code is detected and translated into signals from which the code can be recognized.
  • the above-referenced Eastman et al. Patent may be referred to for further details respecting the operation of a scanner such as shown in FIG. 3C.
  • FIG. 8 shows the transmission function of a bi-segmented mask which is illustrated in FIG. 4.
  • the central stripe 25 has a 100% transmission while the outside stripes 24 and 26 provide transmission at approximately 50%.
  • the relationship of the transmissivity of the different segments may be selected in order to tailor the profile of the beam over the working range of the scanner. In some applications, it is advantageous for the inner segments to have lower transmissivity than the outer segments. It is believed that the light diffracted through the different segments interacts.
  • the amount of partial opaqueness (POP) is varied in order to obtain the smoothest profile.
  • the resolving power of the beam has been extended to read bar codes close to the window of the scanner as well as far away from the window (for example from a range of approximately one inch to thirty inches from the window). Over this range, the effective width of the beam is sufficiently small to be capable of reading high density code (e.g. 10 mil (0.010 inch) minimum bar widths).
  • the outside transmission function (called the edge transmission in FIG. 9) reads codes at the far end of the working range, while the central transmission function reads in closer to the window of the scanner.
  • the bi-segmented transmission mask divides the beam into two segments.
  • the center of the mask cores or cuts out a center region of the beam with the characteristic dimension (a).
  • the edge region of the mask cuts out a second region with a characteristic dimension (A). Consequently, the beam may be thought of as being decomposed into two separate beams that propagate independently. These beams combine in accordance with the principle of superposition.
  • FIG. 10 illustrates the beam size (the width or waist dimension) for each of the beam segments along the resolving axis (the distances (dwa) for the narrower mask segment and (dwA) for the larger mask segment).
  • diffraction causes the beams to decrease in size at a rate greater than predicted by geometrical optics when focused by the converging lens 20. Then the far field diffraction regions commence and the beams diverge at a rate proportional to the reciprocal of the mask segment size (a, A).
  • the mask segment sizes for a two segment mask are selected so that the characteristics (the near and far field diffraction regions) due to the different segment sizes intersect at a point P.
  • There the waist of the beams (w) due to each mask size are equal (dwa2 or the distance in the far field or second region (region 2) due to the smaller mask segment (a) equals the distance dwA1 due to near field diffraction of the larger mask segment (A)).
  • This is denoted on the diagram as P.
  • the point P is the cross over point where the waist size (the size of the beam along the resolving axis - w) is the same for both segments. Then over a distance, indicated in FIG.
  • the beam size along the resolving axis is less than or equal to w and this condition of beam size exists over a significant range close to the window 84 (see FIG. 3C) and extends to a significant distance, e.g. 30 inches from the window.
  • the mask may be provided either by a physical aperture or hard stop or a combination of a physical aperture and the phantom aperture discussed in the Eastman et al. Patent referenced above.
  • the mask may be coated on the face of the lens.
  • FIG. 11 illustrates a diagram similar to FIG. 10 but where a mask such as shown in FIG. 7 comes into play. It will be apparent that there are two intersections and the distance over which the beam has generally constant size across the resolving axis, w, may be extended through the use of additional segments of the mask.
  • v is a constant. Its value matches the theoretically calculated beam width to the experimentally measured beam width. The value of v varies depending upon the modality of measurement (i.e., FWHM or full width half maximum, 1/e 2 points, where e is the base for Naperian logarithms, etc.).
  • Equation (5) defines the desired condition shown in FIG. 10 in which the waist size due to far and near field diffraction are equal at the cross over point P.
  • That size provides a distance dwA2 of thirty-two inches. Therefore, in this example, 10 mil bar code can be resolved over a distance of from seven to 39 inches from the laser assembly 72 (FIG. 3C) or from the window 84 to about two and one half feet from the window 84 the scanner.
  • the segment sizes may be selected using the following computation to obtain values for a & A using the plots similar to FIG. 10 as discussed above, whereas in the equations presented above.
  • DOF depth of field

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Claims (28)

  1. Verfahren zum Erzeugen eines Musters von allgemein monochromatischem Licht, welches ein vorbestimmtes Konfigurationsmuster und eine Orientierung über einen Bereich von Distanzen aufweist, wobei das Verfahren umfasst:
    Projizieren eines Lichtstrahls (18) entlang eines Pfades (12), der sich ausdehnt über den Bereich und
    Ausbilden des Lichts (18), um die Konfiguration und eine Orientierung zu erzeugen in Ebenen, die senkrecht stehen zu dem Pfad innerhalb des Bereichs durch eine Maske (22), die mindestens zwei Segmente (24-32, 34, 35) aufweist, durch welche der Strahl geht,
    dadurch gekennzeichnet, dass
    mindestens zwei Segmente mindestens ein inneres (25, 27, 29, 31) und mindestens ein äußeres Segment (24, 26, 28, 30, 32, 34, 35) umfassen, und wobei die spezifische Durchlässigkeit eines ersten der mindestens zwei Segmente und eines zweiten der mindestens zwei Segmente verschieden ist, und wobei die Verschiedenheit in der spezifischen Durchlässigkeit der Segmente der Maske (22) mindestens zwei Strahlen schafft, welche in aufeinanderfolgenden überlappenden Distanzen überlagert sind, welche den Bereich bestimmen.
  2. Verfahren nach Anspruch 1, wobei der Projektionsschritt ausgeführt wird mit einem Laser und der Ausbildungsschritt ausgeführt wird durch Begrenzen der Intensität des Lichts (18), welches durch ein bestimmtes von den mindestens zwei Segmenten (25, 27, 29, 31) durchgeschickt wird bezüglich des Lichts (18), welches durch mindestens ein anderes der mindestens zwei Segmente (24, 26, 28, 30, 32, 34, 35) geschickt wird.
  3. Verfahren nach Anspruch 2, wobei der Begrenzungsschritt den Schritt der Ausbildung von mindestens einem anderen der mindestens zwei Segmente (24, 26, 28, 30, 32, 34, 35) mit Material umfasst, welches unterschiedliche Durchlässigkeit aufweist, von dem bestimmten der mindestens zwei Segmente (25, 27, 29, 31).
  4. Verfahren nach Anspruch 1, wobei der Ausbildungsschritt ausgeführt wird durch Apodisieren des Lichts in ein Gebiet, durch welches der Lichtstrahl (18) durchgeht, bevor er in den besagten Bereich eintritt, so dass Fernfeld-Beugung aufgrund eines von den mindestens zwei Segmenten (24-32, 34), welches eine kürzere Distanz über den Bereich bestimmt, Nahfeld-Beugung überlagert aufgrund eines anderen von den mindestens zwei Segmenten (24-32, 34), welches eine größere Distanz über den Bereich bestimmt, und wobei die Distanzen teilweise zusammenfallen.
  5. Verfahren nach Anspruch 4, wobei der Projektionsschritt ausgeführt wird, um den Lichtstrahl (18) bereitzustellen als allgemein elliptischen Strahl, welcher seine Hauptachse entlang einer Linie hat, entlang derer die zusammenfallenden Distanzen angeordnet sind.
  6. Verfahren nach Anspruch 4, weiter aufweisend den Schritt der Erzeugung des Lichtstrahls (18) in einem divergenten Strahl, welcher von dem Pfad (12) divergiert unter einem Winkel, welcher bezüglich einer ersten Geraden, die senkrecht zu dem Pfad (12) steht, größer ist als zu einer zweiten Geraden, die auch zu dem Pfad (12) senkrecht steht, welche zweite Gerade senkrecht zu der ersten Geraden steht, so dass der Querschnitt des Strahls kürzer ist entlang der ersten Geraden und länger entlang der zweiten Geraden, und wobei der Apodisationsschritt ausgeführt wird mit der kürzeren Distanz über das Gebiet, das sich entlang der zweiten Gerade erstreckt.
  7. Verfahren nach Anspruch 6, wobei der Erzeugungsschritt ausgeführt wird mit Hilfe einer Laserdiode (10).
  8. Verfahren nach Anspruch 4, wobei der Projektionsschritt ausgeführt wird mit Hilfe einer Linse (20), die einen geometrischen Bildabstand aufweist, welcher mindestens gleich ist dem Quadrat der kürzeren Distanz, dividiert durch die Wellenlänge des Lichtstrahls (18).
  9. Verfahren nach Anspruch 8, wobei der geometrische Bildabstand für die Linse (20) für Licht, welches apodisiert wird, von dem Segment, welches die längere Distanz aufweist, mindestens gleich ist dem Quadrat der längeren Distanz, dividiert durch die Wellenlänge des Lichts.
  10. Verfahren nach Anspruch 1, wobei die mindestens zwei Segmente (24-32, 34) konzentrisch zueinander sind.
  11. Verfahren nach Anspruch 1, wobei die mindestens zwei Segmente (24-32, 34) radial symmetrisch sind um ein Zentrum (12), welches mit dem Zentrum des Lichtstrahls (18) zusammenfällt.
  12. Verfahren nach Anspruch 1, wobei der Projektionsschritt ausgeführt wird mit Hilfe einer Linse (20), welche das Licht parallel richtet, bevor der Lichtstrahl (18) die Maske (22) erreicht.
  13. Verfahren nach Anspruch 1, wobei der Projektionsschritt weiter umfasst den Schritt des Fokussierens des Lichtstrahls (18) mit einem Element (20), welches einen Fokus aufweist an dem Teil des besagten Bereichs, welcher durch Fernfeld-Beugung geschaffen wird am nahen Ende des Teils des Bereichs.
  14. Verfahren nach Anspruch 4, wobei der Apodisationsschritt ausgeführt wird mit den kürzeren und längeren Distanzen über das Gebiet, welches so ausgewählt ist, dass die Konfiguration eine Dimension entlang ihres Querschnitts aufweist, welche allgemein die gleiche ist über mindestens einen wesentlichen Teil des Bereichs.
  15. Verfahren nach Anspruch 14, weiter umfassend den Schritt des Abtastens des Musters über einen Strichcode mit Strichen verschiedener Weite, um zurückkehrendes Licht zu erzeugen, von welchem das Symbol, welches von dem Code repräsentiert wird, erkannt werden kann, und wobei der Apodisationsschritt ausgeführt wird, um die längeren und kürzeren Distanzen auszuwählen, um die Breite des besagten Musters bereitzustellen in der Richtung, in welcher das Muster abgetastet wird über die Weite der Striche des Codes.
  16. System zum Formen eines Laserstrahls in einem Strichcode-Scanner, wobei der Laserstrahl (18) verwendet wird, um die Striche eines Strichcodes abzutasten, und das System angepasst ist, den Laserstrahl zu formen zu einem Querschnitt mit einer auflösenden Dimension in der Abtastrichtung über die Weite der Striche des Strichcodes, dessen Querschnitt hinreichend klein ist, um den Strichcode über einen bestimmten Arbeitsbereich zu lesen von einem Fenster des Scanners, durch welches der Strahl projiziert, wobei das System umfasst:
    eine Maske (22) im Pfad des Strahls (18), die mindestens zwei Segmente (24-32, 34, 35) aufweist, wobei der Strahl (18), durch die mindestens zwei Segmente (24-32, 34, 35) geht, wobei die mindestens zwei Segmente (24-32, 34, 35) dimensioniert sind in einer Richtung entlang der auflösenden Dimension und einer vorbestimmten Beziehung zueinander, um die auflösende Dimension über den Arbeitsbereich zu vergrößern;
    dadurch gekennzeichnet, dass die mindestens zwei Segmente mindestens ein inneres (25, 27, 29, 31) und mindestens ein äußeres Segment (24, 26, 28, 30, 32, 34, 35) umfassen und wobei die spezifische Durchlässigkeit eines ersten der mindestens zwei Segmente und eines zweiten der mindestens zwei Segmente verschieden ist und wobei die Verschiedenheit in der spezifischen Durchlässigkeit der Segmente der Maske (22) mindestens zwei Strahlen bereitstellt, welche in aufeinanderfolgenden überlappenden Distanzen, welche den besagten Bereich bestimmen, überlagert sind.
  17. System nach Anspruch 16, wobei die mindestens zwei Segmente (24-32, 34, 35) eine Gestalt aufweisen, welche verlängert in einer Richtung und schmal in einer Richtung ist, die im Allgemeinen senkrecht darauf steht, wobei die mindestens zwei Segmente (24-32, 34, 35) angeordnet sind in der Nähe einer Linse (20), durch welche der Lichtstrahl (18) geht, wobei die längliche Dimension allgemein entlang der Länge der Striche des Strichcodes orientiert ist und wobei die mindestens zwei Segmente (24-32, 34, 35) länger sind als der Lichtstrahl (18) entlang einer solchen länglichen Dimension der mindestens zwei Segmente (24-32, 34, 35).
  18. System nach Anspruch 16, wobei die mindestens zwei Segmente (24-32, 34, 35) Teil eines optischen Mittels sind, welches eine Linse (20) aufweist, die den Lichtstrahl (18) parallel richtet, wo er durch die mindestens zwei Segmente (24-32, 34, 35) geht.
  19. System nach Anspruch 16, wobei die mindestens zwei Segmente (24-32, 34, 35) Teil eines optischen Mittels sind, welches eine Linse (20) aufweist, welche einen Fokus weiter vom Fenster als das nahegelegene Ende einer Region von Fernfeld-Beugung schafft aufgrund des einen der mindestens zwei Segmente (24-32, 34, 35), welches eine kleinere Größe in einer Richtung entlang der auflösenden Dimension aufweist.
  20. System nach Anspruch 16, wobei die wenigstens zwei Segmente (24-32, 34, 35) allgemein konzentrisch zueinander sind und entlang der auflösenden Dimension innenliegende Segmente (25, 27, 29, 31) und außenliegende Segmente (24, 26, 28, 30, 32, 34, 35) bestimmen.
  21. System nach Anspruch 20, wobei die innenliegenden Segmente (25, 27, 29, 31) eine größere spezifische Durchlässigkeit aufweisen als die außenliegenden Segmente (24, 26, 28, 30, 32, 34, 35).
  22. System nach Anspruch 20, wobei die außenliegenden Segmente (24, 26, 28, 30, 32, 34, 35) eine größere spezifische Durchlässigkeit aufweisen als die innenliegenden Segmente (25, 27, 29, 31).
  23. System nach Anspruch 16, wobei die mindestens zwei Segmente (24-32, 34, 35) im Allgemeinen rektilineare Streifen sind, welche einen mittleren Streifen (25) und Streifen außerhalb des mittleren Streifens (24, 26) umfassen, wobei entweder die innenliegenden oder die außenliegenden Streifen eine größere spezifische Durchlässigkeit aufweisen als die anderen.
  24. System nach Anspruch 20, wobei die innenliegenden (25, 27, 29, 31) und die außenliegenden Segmente (24, 26, 28, 30, 32, 34, 35) konzentrisch zueinander sind und im Allgemeinen kreisförmig sind und wobei entweder die innenliegenden Segmente (25, 27, 29, 31) von größerer spezifischer Durchlässigkeit sind als die außenliegenden Segmente (24, 26, 28, 30, 32, 34, 35) oder umgekehrt.
  25. System nach Anspruch 23, wobei die Streifen (24, 25, 26) nacheinander eine größere spezifische Durchlässigkeit aufweisen, entweder in einer Richtung vom mittleren Streifen (25) zu den außenliegenden Streifen (24, 26) oder von den außenliegenden Streifen (24, 26) zu dem mittleren Streifen (25).
  26. System nach Anspruch 16, wobei die mindestens zwei Segmente (24-32, 34, 35) so dimensioniert sind, dass Gebiete von Fernfeld-Beugung aufgrund des ersten der mindestens zwei Segmente, welche eine geringere Größe in der Richtung entlang der auflösenden Dimension aufweisen, das Gebiet von Nahfeld-Beugung überlappen aufgrund des zweiten der mindestens zwei Segmente, welches eine größere Größe entlang der auflösenden Dimension aufweist, und wobei die Größen des ersten und des zweiten der mindestens zwei Segmente so sind, dass die Gebiete sich in einem Punkt kreuzen, welcher der auflösenden Dimension des Lichtstrahls (18) entspricht, der über dem Arbeitsbereich verbessert ist.
  27. Verfahren nach Anspruch 3, wobei der Ausbildungsschritt ausgeführt wird durch Aufbringen lichtabsorbierenden Materials auf der Oberfläche eines optischen Elements (20).
  28. Verfahren nach Anspruch 3, wobei der Ausbildungsschritt durch Diffusion von lichtabsorbierendem Material in das Material eines optischen Elements (20) ausgeführt wird.
EP94921931A 1993-06-07 1994-06-03 Vorrichtung zur verbesserung der schärfentiefe eines strichmarkierungslesers Expired - Lifetime EP0702817B1 (de)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US08/073,368 US5386105A (en) 1993-06-07 1993-06-07 Diffractive optical beam shaping methods and apparatus for providing enhanced depth of working range of bar code scanners
PCT/US1994/006330 WO1994029815A1 (en) 1993-06-07 1994-06-03 Apparatus providing enhanced depth of bar code reading range
US73368 2002-02-13

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EP0702817A1 EP0702817A1 (de) 1996-03-27
EP0702817A4 EP0702817A4 (de) 1998-08-12
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CA (1) CA2164506A1 (de)
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MX (1) MX9404240A (de)
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KR960702919A (ko) 1996-05-23
EP0702817A4 (de) 1998-08-12
TW244388B (de) 1995-04-01
WO1994029815A1 (en) 1994-12-22
JPH08511639A (ja) 1996-12-03
DE69431435D1 (de) 2002-10-31
US5386105A (en) 1995-01-31
AU671233B2 (en) 1996-08-15
AU7244694A (en) 1995-01-03
BR9406792A (pt) 1996-01-30
EP0702817A1 (de) 1996-03-27
MX9404240A (es) 1995-01-31
DE69431435T2 (de) 2003-05-22
CA2164506A1 (en) 1994-12-22

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